It is proposed to characterize avian leukosis virus especially with respect to their transforming activity for hematopoietic cells. BIBLIOGRAPHIC REFERENCES: Vogt, P.K. (1976). The oncovirinae--a definition of the group. In: "WHO Center for Collection and Evaluation of Data on Comparative Virology, Report No. 1, P. Thein, ed. pp. 327-229, Munich, (1976). Hayman, M.J., Hunter, E., and Vogt, P.K. (1976). Inhibition of avian sarcoma virus replication by glucosamine: A specific effect on the synthesis and processing of viral proteins. Virology 71, 402-411.